First noble gases measurements in lherzolites from Mt Vulture volcano: new constraints on the mantle below Italy

Mount Vulture is a stratovolcano (age 0.75-0.14 Myr) located in southern Italy, which despite being at the same latitude of Vesuvius and Phlegreian Fields, has several peculiarities about its setting and erupted magma composition. Indeed, if compared to other Italian Quaternary volcanoes, it is the only one located east of the Apennine Front, about 100 km off the axis of the Campanian Magmatic Province (Peccerillo et al., 2017). Furthermore, although being a quiescent volcano (last eruption dated 0.14 Myr), previous studies (e.g., Caracausi et al., 2015, Bragagni et al., 2022) have shown extremely high CO₂ emissions (4.85 × 108 mol yr^-1), which are likely related to the carbonatitic volcanism of its final phase of activity, as well as some petrological aspects in the erupted products pointing to a mantle source metasomatism.

Recently, investigations on Vulture mantle xenoliths (Carnervale et al., 2022) revealed CO₂-rich fluid inclusions (FIs) that indicate a primary depth of bubbles entrapment in olivine and pyroxene phenocrysts coinciding with the regional crust-mantle boundary (27-30km).

This research focuses for the first-time noble gases isotopes (He, Ne, Ar) in FIs from lherzolite enclaves from Mt. Vulture tephra. The He isotopic ratios (as R/Ra; R is the ³He/⁴He ratio of the sample and Ra the same ratio in air), are between 6.2 and 5.4 ± 0.08. These values are lower than the signatures of the MORB upper mantle (8 ± 1Ra) and overlap the values of the Sub Continental Lithospheric Mantle (SCLM, 6.1 ± 0.9Ra). The Ne isotopic signatures (²⁰Ne/²²Ne and ²¹Ne/²²Ne) are in the field of the MORB values.

The He-Ne-Ar systematics is consistent with a SCLM source feeding the magmatism of the Vulture volcano. However, considering the noble gases He-Ne-Ar, in Vulture xenolites this mantle source has affinities with that feeding the volcanic activities of Mt. Etna (Nakai et al., 1997; Correale et al., 2014). This inference bears some evidence about the similitudes of the mantle below these two volcanic systems that is affected by mantle metasomatism, which is likely also responsible for the large CO₂ fluxes and the carbonatitic magmatism (Bragagni et al., 2022). New measurements of the noble gases in free gases from the two volcanoes together with a detailed comparison between the geochemistry and petrography of the Vulture and Etna most primitive products will provide new constraints on the mantle typology below the two volcanoes and its relationship with the geodynamical evolution of the central Mediterranean.

References

Bragagni et al., 2021, Geology

Carnevale et al. (2022). Geophys. Res. Lett.

Caracausi et al. (2015). Earth Planet. Sci Lett.

Correale et al., 2014. Lithos

Nakai et al., (1997). Earth Planet. Sci Lett.

Peccerillo, A. (2017). Advances in Volcanology. Springer, Cham.